Do you see any terms canceling each other? There should be many.
If you can't see, write them in two different lines, and let the same terms (x, x^2, x^2,...) come one top of another and see how they cancel each other.

Differentiate equation (1) with respect to x
must be:
Differentiate equation (1) with respect to r.

-O

Aw rats! The deliberate mistake I always make to see if the OP thinks about and understands what I post has been exposed. Second time this week it's happened, dran it. Now I gotta go fix it and put in a new mistake ....